While pressure-sensitive adhesive (PSA) tapes were introduced to the market more than fifty years ago, the problems associated with adhesive transfer from "faceside" to "backside" of the tape backing were not seriously addressed until the 1950's. By that time, continuous improvements in the adhesive coatings and the introduction of non-fibrous, film-type backings introduced problems associated with the ease of release without attendant loss of adhesion. These problems were addressed by the teachings found in a variety of PSA tape patents. Outstanding among these patents, principally directed to low adhesion backsizes (LAB) were U.S. Pat. No. 2,496,349, which disclosed a hydrocarbon wax-butyral composition; U.S. Pat. No. 2,532,011 introduced a polyvinyl carbamate composition; U.S. Pat. No. 2,607,711, which disclosed a copolymer of a higher-alkyl acrylate or higher-alkyl methacrylate monomer ester and at least one ethylenically unsaturated monomer (preferably acrylic acid or methacrylic acid); U.S. Pat. No. 2,876,894, which disclosed a vinyl stearate/maleic anhydride release coating; and U.S. Pat. No. 3,318,852, which was the first commercial embodiment of an LAB utilizing a fluorine-containing copolymer.
At about the same time that the LAB coatings were being developed, problems were being noted in connection with PSA tape backings which were alleged to be "directly printable". Initially, paper backings were reasonably easy to print and the inks utilized therewith were similar to those from other paper printing applications. When the non-fibrous, film tape backings appeared, new problems became apparent. Such problems were solved in a variety of ways. Virtually thousands of ink formulations were developed to meet the requirements which were peculiar to printing on flexible film tape backings, which were marketed in roll form. Today, there are many well-known so-called flexographic inks.
Problems with direct printability varied from the hydrophilic backings of the regenerated cellulose-type, the less polar cellulose esters, plasticized or unplasticized polyvinyl chloride, and polyesters, to the hydrophobic polyolefins. These backings were employed in applications which required high tensile strength and resistance to unfavorable environments.
At this time, patents began to appear which dealt with printable tapes of varied backing compositions. Modifications of release properties and anchorage properties for the printed image were accomplished by additives included in the backsize coatings or by multilayered coatings followed by post-treatment of the printed tape to enhance image anchorage. U.S. Pat. No. 2,819,169 discloses a methacrylate "mirror coating" which assertedly permits conventional flexographic inks to be printed on cellulose acetate film backings where the PSA utilized is a natural or synthetic rubber composition. This patent also discloses a slightly less effective nitrocellulose "mirror coating".
Canadian Pat. No. 772,120 relied upon a thin ethyl acrylate/methacrylate copolymer coating to provide a printable unplasticized polyvinyl chloride-backed PSA tape; German OLS No. 2,018,929 discloses a printable and releasable backsize comprised of a blend of ethyl acrylate/methyl methacrylate and vinylidine chloride/acrylonitrile which was limited to polyvinyl chloride backings. In U.S. Pat. No. 3,543,920 there is disclosed a copolymer of stearyl methacrylate/acrylonitrile which is used as a compatible release material with standard film formers to provide a printable surface for paper and polyester film backings.
U.S. Pat. Nos. 3,681,105 and 3,773,538 disclose "transfer-proof" inks for PSA tape backings which utilize surface active compounds comprised of perfluorinated alkyl groups and complexes of fatty acids with aluminum, chromium or titanium in combination with conventional flexographic ink film binders to assertedly prevent offsetting of the ink from cellophane film.
U.S. Pat. No. 3,967,031 discloses a printable PSA tape which uses a blend of cellulose acetate butyrate and a copolyester or acrylic ester to provide "low unwind" and printability for unplasticized polyvinyl chloride and polyester backed films. U.S. Pat. No. 3,978,274 discloses a smoother unwind of a printable PSA tape by employing a ternary resin system of a vinyl film former, a hard thermoplastic acrylic resin and a polyamide plasticizing resin alleged to perform well with cellulose acetate and polyester film backings. U.K. Pat. No. 2,116,074 discloses a printable polypropylene-backed PSA tape which is obtained by a process which involves (a) corona priming of polypropylene backing, (b) coating with a lacquer based on (1) acrylate-chloroaceto-vinyl, or (2) polyurethane or (3) polyamide; then (c) printing thereon with a flexographic ink; and finally, (d) overcoating with a release coating of polyvinyl carbamate-based release material.
Despite the considerable prior art in the problem areas discussed above, there is no teaching of the unique combination of an LAB of excellent efficiency in combination with ink anchoring and primer resins. By combining these normally incompatible components to prepare a backsize solution which can be applied as a coating in a single step, I have accomplished a feat which has long been desired.